Synchronized multi-wavelength picosecond pulse generation by a single-frequency laser seeded Raman fiber amplifier

Synchronized multi-wavelength ultrafast laser has been widely used in Raman scattering spectroscopy, ultrafast pump-probe microscopy, coherent optical synthesis, and difference-frequency generation. Here, we demonstrate a cascaded single-frequency continuous wave (SF-CW) laser seeded Raman fiber amplifier to generate synchronized multi-wavelength picosecond pulses centered at 1065 nm, 1121 nm, and 1178 nm with ∼10 ps pulse duration. Different from the previous reported methods with resonator configuration, the SF-CW seeded Raman fiber amplifier not only is free of elaborate cavity length alignment but also presents repetition rate agility. Utilizing a gain switched diode as the pump source, the repetition rate of the synchronized multi-wavelength pulses could be adjusted from 20 MHz to 50 MHz. Additionally, the influence of the amplified spontaneous Raman emission (ASRE) has been investigated experimentally. It was found that suppressing the accumulated ASRE from the preceding amplifier stage is the key to obtain high-order Stokes pulses with decent spectral coherence.